Friction-enhanced lifetime of bundled quantum vortices

Abstract

Experiments in the early 1980s have shown that a compact bundle of quantum vortex rings in superfluid helium remains coherent and travels a significant distance compared to its size. This is surprising because a single vortex ring, under the effect of friction with the background of thermal excitations (the so-called normal fluid), would quickly lose energy and decay. The observation of these long-lived vortex structures has remained an unsettled question since their experimental detection. In this work, by taking into account the fully coupled dynamics of superfluid vortices and the normal fluid, we show that the motion of the superfluid bundle generates a large-scale wake in the normal fluid which reduces the overall friction experienced by the bundle, enhancing its lifetime. This collective effect is similar to the drag reduction observed in systems of active, hydrodynamically cooperative agents such as bacteria in aqueous suspensions, fungal spores in the atmosphere and cyclists in pelotons.

Superfluid drain vortex

“…The drain flow twisted bundle is similar to other twisted vortex states which have been observed in superconductors [12], and, more relevantly, in rotating 3 He [13] and large-scale 4 He vortex rings [14][15][16]. Finally, by combining order (the strong axial polarization) with a controlled amount of disorder (induced by the radial drain flow), our results show that this bathtub vortex flow is a promising configuration to develop theoretical tools based on the HVBK equations and Vinen equation [17,18] to model problems of rotating quantum turbulence [19], ranging from liquid helium counterflow [20,21] to neutron star glitches [22,23] to atomic gases [24].…”